DISCUSSION ON THE CHARACTERISTICS AND SEISMO-TECTONICS OF THE GAIZHOU ML 4.7 EARTHQUAKE SWARM SEQUENCE ON FEBRUARY 2, 2012

doi:10.3969/j.issn.0253-4967.2013.04.013

Abstract

Abstract: During the Gaizhou M_L4.7 earthquake swarm sequence on February 2,2012,the energy release weakened gradually with time,accompanied with two obviously accelerated release processes. The double-difference location results show that the spatial distribution of Gaizhou earthquake swarm is mainly concentrated in the area between the Jinzhou Fault and the Yingkou-Haicheng Fault,spreading roughly in NW direction. The sequence showed a trend of migrating from Jinzhou Fault to Yingkou-Haicheng Fault,and the focal depths are distributed from 6km to 9km.
The P-axis directions of focal mechanism of the two M_L 4 earthquakes occurring on February 2 are distributed from 94 to 120 degrees,which coincide with the previous studies on the regional tectonic stress field. We could infer that Gaizhou M_L 4.7 earthquake sequence on February 2 was caused by the strike-slip faulting of Jinzhou Fault under the action of NWW or near-EW regional stress field. But the P-axis direction of the two M_L 4 earthquakes occurring on July 12 and November 1 turned to near NS,and according to the precise relocations,these two earthquakes had the trend of migrating to Yingkou-Haicheng Fault. It is inferred,therefore,that the two obvious stress releases are not only the result of slip of Jinzhou Fault,the Yingkou-Haicheng Fault also played a certain role.
Combining with acoustic emission results,it can be further found that seismogenic structure of the M_L 4.7 earthquake swarm in Gaizhou is the two en echelon faults,the NE-trending Jinzhou Fault and the Yingkou-Haicheng Fault. This earthquake swarm could be caused by joint action of the two faults. Meanwhile,it also indicates that there are signs of activity of both Jinzhou and Yingkou-Haicheng Faults under the action of the regional stress field.

Key words: double-difference location, earthquake swarm sequence, en echelon fault, acoustic emission, seismo-tectonics

摘要： 2012年2月2日盖州M_L4.7震群序列随着时间的推移能量释放有逐渐减弱的趋势，期间有2次明显的加速释放过程。双差定位结果显示，盖州震群空间分布主要集中在金州断裂和营口-海城断裂之间，大体呈NW向展布，序列随时间有从金州断裂向营口-海城断裂迁移的趋势，震源深度大部分集中在6～9km。2月2日发生的2次4级地震的震源机制解P轴方位为94°～120°，这与前人对这一地区区域构造应力场研究的结果基本吻合，表明2月2日发生的盖州M_L4.7地震序列是在NWW或近EW向区域应力场作用下，金州断裂走滑错动的结果。但7月12日和11月1日的2次4级地震的P轴方位转变为近NS向，且从精定位结果来看，这2次地震有往NW向营口-海城断裂迁移的趋势，由此推测这2次明显的应力释放过程不单纯是金州断裂滑动的结果，营口-海城断裂也起了一定的作用。声发射等实验结果进一步表明，盖州M_L4.7震群的发震构造为NE向的金州断裂和营口-海城2条雁行断裂。该震群的发生可能是金州断裂和营口-海城断裂共同作用的结果，同时也表明在区域应力场作用下，金州断裂和营口-海城断裂有活动的迹象。

关键词: 双差定位, 震群序列, 雁行断裂, 声发射, 发震构造

CLC Number:

P315.6

CAO Feng-juan, WANG Liang, JIAO Ming-ruo, ZHAI Li-na, WANG Yan. DISCUSSION ON THE CHARACTERISTICS AND SEISMO-TECTONICS OF THE GAIZHOU M_L 4.7 EARTHQUAKE SWARM SEQUENCE ON FEBRUARY 2, 2012[J]. SEISMOLOGY AND GEOLOGY, 2013, 35(4): 842-852.

曹凤娟, 王亮, 焦明若, 翟丽娜, 王岩. 2012年2月2日盖州M_L4.7震群序列特征及发震构造探讨[J]. 地震地质, 2013, 35(4): 842-852.

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